An adjective is a word that describes a noun. There are two kinds: attributive and predicative. An adjective is used attributively when it stands next to a noun and describes it.
For example: The black cat climbed a tree.
Notice that the verb participle forms can be used as adjectives:
The man felt a paralyzing fear.
Flavored oatmeal tastes better than plain oatmeal.
The usual place of the adjective in English is in front of the noun. You can have a whole string of adjectives if you like: The tall thin evil-looking cowboy roped the short, fat, inoffensive calf.
Sometimes, for rhetorical or poetic effect, the adjective can come after the noun:
Sarah Plain and Tall (book title)
This is the forest primeval.
An adjective is used predicatively when a verb separates it from the noun or pronoun it describes:
The umpire was wrong.